"I felt pretty confident with my answers on both questions and perhaps that worked against me with the second equation," Lt Gruber admitted.

Indeed, more than a few people have pointed out the answer he gave to the second, more complicated question, was incorrect - but the Police Department in Marion, Ohio, are still seeing the episode as a win.

"We are nailing our goals of increasing trust, transparency & being approachable. Still a work in product on the math skills," the force wrote on its Twitter page after Lena's mum Molly uploaded screenshots of the conversation to Facebook.

The post has now been liked more than 2,300 times.

"We really hope that are are not flooded with homework requests... so far, so good," Lt Gruber said.

"We really see this not different that a child walking up to an officer on the street and asking for help. This is just a 21st Century version of that interaction. We do however encourage kids to communicate with parents, teachers, siblings and fellow students before asking us."

As for Lena, she knows she can't always rely on the police to help her with her homework. But she does have a backup plan.